Method for manufacturing synthetic leather



United States Patent 01 3,424,604 Patented Jan. 28, 1969 3,424,604METHOD FOR MANUFACTURING SYNTHETIC LEATHER Osamu Fukushima, HiroshiHayanami, and Kazuo Nagoshi, Kurashiki, Japan, assignors to KurashikiRayon Company Limited, Kurashiki, Japan No Drawing. Filed Nov. 9, 1964,Ser. No. 409,997 Claims priority, application Japan, Nov. 15, 1963,38/61,338; Dec. 11, 1963, 38/66,746; Jan. 29, 1964, 39/3,956 US. Cl.117-11 28 Claims Int. Cl. 133% 5/02; D06m 15/ 00 ABSTRACT OF THEDISCLOSURE A method for making an air and moisture-permeable sheetmaterial comprising impregnating a fibrous substrate of mix-spun fiberswith an impregnant comprised of a high molecular weight polymericmaterial having rubber-like elasticity, coagulating the impregnant, andextracting one of the polymers in the mix-spun fibers by means of asolvent which is a non-solvent for at least one other polymer in thesaid mix-spun fibers.

The present invention relates to a pliable, airand moisture-permeablesheet material with a high strength and to the method of manufacturingthe same. In particular, the invention is concerning with a sheetmaterial which bears a striking resemblance to the natural leather instructure, external appearance, texture and touch, that is so-calledsynthetic leather, and with the method of preparing the same.

The novel commodity, so-called synthetic leather, has come to the objectof attention in the world market in recent years, and in Japan, withoutexception to the rule, this has brought about a certain boom.

For a long time, the manufacture of synthetic articles having the samecomposition as that of the natural leather has been a dream for theskilled in a certain art. First, there has been produced the so-calledregenerated leather by the method which comprises the two basic steps ofcrushing a scrap of natural leather and dissolving the resulting crushedleather, from the economical view point of utilization of scraps ofnatural leather rather than the view that the synthetic article shouldbe of the same composition as that of the natural one. Next, as anattempt to provide a similar characteristic to the natural leather tothe resulting article, even a camouflage has been effected by giving asimilar odor to that of the natural leather to the regenerated leather.Among these attempts, there was continued to make researches on theregenerated leather, and in a certain field the regenerated leather hasbeen put into practical use in place of the natural leather and thereare a number of technicians who have an expectation that the regeneratedleather will be put into practical use in another field. In spite ofsuch efforts, however, the first ideal has not been realized because ofdifliculty in synthesizing proteins which are principal constituent ofthe natural leather and of the fact that the obtained leather has someunfavorable characteristics, and it is not conceivable that the firstideal will be realized in the recent future and the production of theregenerated leather will be industrialized.

Under such conditions, as article heretofore regarded as a substitutefor the natural leather, there has been the artificial leather,so-called imitation leather. The artificial leather was made, in theearly time, by coating nitrocellulose and then vinyl chloride or rubberby changing the coatings on woven fabrics. The artificial leather ismade resembling to the natural leather in the texture by composing ofthe coatings and in the external appearance by pressing grain. Thephysical strength of the artificial leather, however, depends only uponthe fabric used.

The recent development of the plastic industry, however, has resulted ina group of worked fabrics, so-called synthetic leather, which exceed thestage of imitation leather by bringing about various plastics which arenot inferior to the natural leather in physical strength and chemicalresisting property in the original material field, by proposing to usenon-woven fabrics in place of the woven fabrics structurally in thespinning industry and by applying a method of producing microporoussponge or a wet process wherein film is formed in a liquid medium inplace of a dry process in the technical field of working and processing.The so-called synthetic leather is competing with the natural leather ina certain field and is being used in a larger quantity than the latterin the manufacture of certain goods as it excels the natural leather insome properties and is less expensive than the latter. It seems,however, that any one of the industries is not satisfied by thesynthetic leather now on market, in Japan as Well as in foreigncountries, because of its unsatisfactory external appearance andcharacteristics. In particular, in the shoe manufacture, the syntheticleather is so inferior to the natural leather that there is an intensedemand for investigations on and opportune development in appropriatematerials and constituents.

In Japan, the shoe makers first demanded a synthetic leather with anexternal appearance and touch similar to those of the natural leatherand this demand was comformable to the other industrial fields intendedto use the synthetic leather, so that it has been regarded as the firstrequirement that the synthetic leather resembles to the natural leatherin external appearance and texture and, contrarily, workability andother characteristics of the synthetic leather have been considered tobe of the secondary. At the present time, however, the demand has beenmoved from the appearance to the qualities and there is a demand forsynthetic leathers which are superior in qualities to the natural one.

The deficiencies remaining on the natural leather are the very problemsalso on the synthetic leather, upon estimation of the latter. Thus, itneeds making clear the advantages and defects of the natural leather forexact estimation of the synthetic leathers. Briefly speaking, the novelsynthetic leather should retain desirable properties of the naturalleather but be free from undesirable properties of the latter.

Considering the structure of the natural leather, the dermis is the mainpart constituting the leather which substantally determines itsqualities, the epidermis defines the external appearance, and thehypodermis, the so-called hypodermal fatty tissue, makes thecharacteristic back surface of the finished leather as the hide isstripped off at this part. The dermis is composed of collagen, and thecharacteristics of the leather attributable to the collagen are asfollows:

(1) Collagen fibers, in the dermis, are intertwined with all angles tothe surface of the dermis to form a firm net-work.

(2) The collagen fibers retain pliability even if dried completely toremove therefrom moisture and scarcely break if flexed in any direction.

(3) The collagen fibers adjacent to the papillate surface are extendingin parallel to the surface of the leather and are more compact than theinternal reticulating tissue and, in addition, elastic fibers spread inthe interior, so that they serve for preventing the surface of theleather from crack and for imparting to the surface of the leather agrain.

(4) Each collagen molecule has a mild linear structure, moreparticularly a spherical configuration, and some molecules collecttogether to form, by degrees, a micelle, a fibril, a visible fiber andfinally a tridimensional fiber.

The availability of the leather is not attributable to its individualproperties and features but to the excellence of the combination of theindividual properties. This is a remarkable feature ofthe leather whichcan not be found in the other materials and, moreover, the leather, dueto a natural product, has such several specific characteristics that onecan not limitate. On the other hand, some defects on the leather areregarded as peculiar to the leather, but these result from the commonproperty of the natural article. Therefore, it is essential for thoseskilled in the synthetic leather to surely know the advantages anddefects of the natural leather, and the following items commonly may bespecified as common sense. Among these, the advantages are, connected tothe appropriate properties and Working ability for leather material formaking shoe and the defects indicate the problems to be noticed upondesign of synthetic leathers.

As the advantages may be specified the following points:

(1) The leather has a unique beauty attributable to its grain surface.Commonly the expression leather-like has been used, and leather-madeornaments match Well both Japanese clothes and European clothes.

(2) The leather possesses great, balanced mechanical strength. Thetensile strength and tear strength of the leather are greater than thoseof the other materials which resembles in other properties to theleather and would be employed in the same uses as that of the leather,and there is not found any differential in the strength between thelongitudinal and lateral directions as found in the other materials.

(3) The leather exhibits a unique tension-elongation curve, to say, theleather has a greater modulus than the other materials employed in thesame uses, and the differential in tensile strength and in elongationbetween dry state and wet state is not so great as in the othermaterials in spite of great differentials in the other properties.

(4) The leather is pliable, readily gets to fit and has a small specificgravity. These indicate that the leather has a high flexibility in theshape and a high adaptability in the working.

(5) The leather has proper moisture-absorbing property and moistureandair-permeabilities. The development of the function combined theseproperties is an essential property for raw material of products useddaily, and in a highly humid environment as in Japan.

(6) The leather has temperature retaining and heat insulatingproperties. It is evident from its structure that in addition to theabove described properties are added, and this makes it excellent heatinsulating materials to be used in the winter season.

(7) The leather is capable of being formed into a product with a desiredcurved surface. This indicates the leather having an excellentworkability, and it is said that the harmony in resiliency and creepingproperty is the characteristic of the component of the leather.

(8) Cutting operation is easy. Though the tissue is compact and layershaving different densities are laminated, the fact that the leatherpossesses such properties may be attributable to the composition ofvarious constituents.

(9) The leather is dyeable with case. This indicates that thecomposition in grain surface, is compact and uniform and that theleather may be suitably used as material for personal ornaments andwears.

As the defects may be specified the following points:

(1) The leather is different in properties according to the race ofanimal and the area living the animal, and even in the same race ofanimal the properties of the leather are different depending upon thesex, age, feed, season and other factors, and in one piece of leatherthe properties differ according to portions.

(2) The leather is different in size and thickness from piece to piece,so that it has been handled manually and it is of difficulty to handlethe leather by machines.

(3) The leather is, as mentioned above, restricted in size and the partshaving the same property are small, so that it is of difficulty to cut apatch with a desired shape from a piece of leather, and this influenceshighly upon the cost.

(4) For this reason the leather is not inexpensive and, in addition, theleather is not manufactured as an industrial material for the mainobject but it is byproduct of the meat, so that an amount of the leathersupplied is influenced by the weather and the demand condition of meatsand the price is varied.

(5) In conversion of hides to leathers there is needed both a longperiod of time and a complicated tanning technique, and the productioncontrol and quality control in the tanning industry is of diflicultybecause the fundamental investigation on the protains in the raw hideand on the functions and actions in the tanning process has not yet beenaccomplished.

(6) It is a difficult matter to stabilize the leather againstdeterioration and vermin damage under a high humid condition as in Japanbecause the leather is a natural product and is composed essentially ofproteins.

These defects are essential to the leather that is a natural product.Accordingly, it is supposed to be a task for one who intends to makesynthetic leathers to eliminate such defects as found in the naturalleather, to improve such advantages as in the natural leather withoutany depression in the other properties and, thereby, to improve thecombined properties.

An object of the present invention is to provide a synthetic leatherwhich retains the advantages of the natural leather and is improvedfully in the defects of the latter and the method of preparing suchsynthetic leather.

Briefly speaking, the synthetic leather of the present invention may beobtained by forming a web or fibrous mat with a mix-spun fibercomprising at least two high molecular weight materials, impregnatingthe web with a solution of one or more high molecular weight materials,coagulating the impregnating substance in a wet or dry process and,thereafter extracting and removing at least one high molecular weightmaterial which constitutes the mix-spun fiber by treating said web in asolvent for at least one of the high molecular weight materialsconstituting the fiber.

The mix-spun fiber may be obtained by a wet, dry or melt spinning of amixture of two or more high molecular weight materials, although themelt spinning process is preferable. Preferably the filament isstretched after spun.

Examples of the high molecular weight materials used are polyolefins,such as polyethylene and polypropylene; atacticand isotacticpolystyrenes, alkyl or halogen substituted polystyrenes; polyamides,such as 6-nylon and 66-nylon; polyesters, such as polyethyleneterephthalate; polymethacrylates such as polymethylmethacrylate;polyvinyl esters such as polyvinyl acetate and polyvinyl butylate;polyvinyl alcohol and its derivatives; polyvinyl halides such aspolyvinyl chlorides; polyacrylonitrile; polyvinylidene halides such aspolyvinylidene chloride; cocondensates or copolymers comprising variouslow molecular weight condensated or polymerized materials and graft highmolecular weight materials as obtained by graft polymerization ofvarious polymerizable low molecular weight substances with the varioushomopolymers or cocondensates or copolymers thereof. Of course, whenselecting two or more high molecular weight materials, they must be ableto mix-spin. The term be able to mix-spin means that it is required tohold the fibrous form when spun, but does not always mean that theresulting filament must have a uniform internal structure. It ispreferable that the mix ratio of these mix-spun fiber is 20% or more ofone high molecular Weight material with respect to the other material.The high molecular weight material to be removed and extracted in themix-spun fiber preferably is swollen with or dissolved in the solvent inthe solution of the high molecular weight mate rial to be impregnated inthe mat and, in this case, there is obtainable a satisfactorily compactsynthetic leather due to a press effect during the coagulating step.

Then a web or fibrous :mat in a wet or dry process from the resultingmix-spun fiber. The web or fibrous mat thus formed is too coarse andwhen desiring to obtain a final product with a high strength, the web orfibrous mat may be tightened in a suitable manner. This processpreferably is carried out as follows: The mix-spun fiber is cut into astaple, which is formed into a random web by means of a random webber.The random web is then tightened and three dimensionalized by means of aneedle punch. When the tightening is insufficient, the web is furthertightened by compression. It is preferable to heat the web during thecompression. The tightening also may be effected by application ofshrink to the fibers. The demand to obtain a final product with a highstrength may be attained by stretching the sheet material withoutallowing any shrinkage.

'Ilhe present invention has a distinctive feature in the process formanufacture of such three-dirnensionalized non-Woven fabric. In themanufacturer of a good synthetic leather from a three-dimensionalizednon-woven fabric, it is a fundamental condition that the mat is pliantand supple. To obtain a pliant and supple mat, it is preferred to use afiber with a fine denier less than 1 denier, preferably less than 0.5denier. It is, however, difficult to form a random web by passing suchfine fiber through a card sliver and to form a three-dimensionalizednon-woven fabric therefrom by means of a needle punch because of a poorspinnability of such fine fibers.

Contrary to these facts, in the present invention there may be used awell-spinnable fiber of from 1.5 to 3.0 denier to form a mat. A thickfiber with a denier as large as from 1.5 to 3.0 denier is far superiorin spinnability to a fine fiber with a denier as small as 0.5 denier orless. A mat which has been made from a large fiber with a denier of aslarge as from 1.5 to 3.0 denier is in general not pliant, but at leastone high molecular Weight material within the fiber is extracted andremoved in a subsequent extraction process, whereby it is possible toobtain a mat having the same pliability as that of mat made from a finefiber with a denier of about 0.5 denier.

In the present invention a fibrous mat is made from a mix-spun fibercomposed of two components, one being soluble and another beinginsoluable in the subsequent step. This brings about an additionaladvantage. To say, when manufacturing a mat from a fiber obtained aloneone high molecular weight material, if the fiber is poor inspinnability, so that it is difiicult to manufacture a mat, to said highmolecular weight material and the mixture is spun to obtain a mix-spunfiber having a good spinnability, from which a mat is manufactured. Forinstance, a fiber formed of a 6-nylon alone has a poor spinnability dueto its low Youngs modulus and to its unsuitable dryto-wet ratio inYoungs modulus. As mentioned above 6- nylon fiber having a fiber denierassmall as 0.5 denier is very ditficult in the spinnability. On thecontrary, a mixspun fiber formed of a mixture of a 6-nylon and apolystyrene has an improved Youngs modulus and wet-todry ratio in Youngsmodulus as shown in Table 1.

TABLE I Mix ratio P0lystyrene O 10 20 30 40 50 60 fi-nylon 100 90 80 70(i0 50 4O Youngsmodulus {Dry(g./d.) l. 18 21 24 3O 33 36 40 Wet (g.ld.)10 21 23 25 30 33 38 ness of about 0.5 denier makes possible to form athreedimensional non-woven fabric without any difiioulty, by employingconventional equipments and under conventional processing conditions,because of a remarkable improvement in spinnability and of an improvedseparability from carding machine.

The web or sheet material so formed in the above steps is impregnatedwith a solution of a high molecular weight material. The high molecularweight material includes: (1) one or more high molecular weight materialhaving rubber-like elasticity and (2) mixtures of one or more highmolecular weight material having rubber-like elasticity with one or morehigh molecular weight materials having no rubber-like elasticity. Thesolution need not be a true solution, but may be an emulsion as far asit is possible to impregnate the web therewith. To the solution theremay be added salts, dyes, pigments, fillers, various surface activeagents and other additives.

As those materials are used any of such ones which are insoluble in thesolvent to be used in extraction of an eX- tractable high molecularWeight material in the mix-spun fiber. Examples are polyurethanse-typeelastic high moleoular weight materials, acrylates, syn-thetic rubbers,chlorinated polyethylene and polyolefin derivatives, internallyplasticized high molecular Weight materials and other elastic highmolecular weight materials having a rubbery elasticity.

As the high molecular weight material having no rubbery elasticity, usemay be made of various polymerized or condensated high molecular weightmaterials such as polyvinyl chloride, polyacrylonitrile, polystyrene,polyvinyl alcohol or acetalized product thereof, polyvinyl acetate,polyamides, modified polyamides, polypropylene, polyethylene,polyurethanes, polyureas, polyesters, polycarbonates or cocondensated orcopolymerized materials thereof, or graft polymerized high molecularweight materials.

After impregnation of the web with the high molecular weight material,the impregnated material is coagulated in a wet and/0r dry process. Itis preferred to press or hot press the impregnated sheet material eitherbefore, during or after the coagulating process.

The sheet material is then treated with a solvent to extract therefromat least one of the high molecular weight materials which are componentsof the mix-spun fiber forming the sheet material. It is preferable toremove by extraction, before, during or after the extracting step, apart of the impregnated high molecular weight materials capable ofextracting and removing and a ortion of a coating film which has beenapplied to a grain surface as hereafter described.

The solvent to be used in the 'invention for extraction of at least oneof the high molecular weight materials which constitute the mix-spunfiber should be solvent for at least one high molecular weight material(soluble component) but non-solvent for the remainder (insolublecomponents) of the high molecular weight materials forming the mix-spunfiber. Although the solvent suitably used in the extraction varies withthe nature of the mixspun fiber as a raw material of the artificialleather of the invention, there may be used water, organic solvents,such as aromatic compounds, cyclic ethers, aliphatic hydrocarbons,ketones, cyclic ketones and the like; various salt solutions, such asmethanol solutions of calcium chloride, titanium tetrachloride, lithiumchloride and the like; and mixtures thereof.

The synthetic leather of the invention thus obtained is composed of alayer of fiber which retains a complete fibrous structure as in thenatural leather, and the synthetic leather of the present invention issimilar in external appearance, texture, touch and other characteristicsto the natural leather. The synthetic leather of the present inventionaccomplishes to the problems for synthetic leathers as fully describedat the head of this specification.

The fact that the synthetic leather of the invention is comparable withor surpasses the natural leather in all aspects is based on the integralstructure and the characteristics of the structure will be mentionedhereinafter.

One of the characteristics of the synthetic leather of the invention isthat the fiber, which constitutes the leather, has numbers ofmicro-pores and a grain surface as a result of extraction of at leastone of the high molecular weight materials forming the fiber. This makesthe synthetic leather of the invention very pliant and similar instructure to the natural leather.

As causes for this result may be stated are: that the fiber iself ismade more pliant by the micro-pores therein formed and that the solublecomponent of the fiber exposed to the surface of the fiber is extractedto form a number of spaces between the impregnated materials and thefiber and 'whereby the fiber separates the high molecular weightmaterials having rubbery elasticity to become movable each other. Themicro-pores and spaces result in essential improvements in airpermeability, moisture permeability and air-retaining property and inthe natural leather-like texture.

A large number of micro-pores of the shaped article of the invention isnot only based on spaces formed between the fibers each other composedof the shaped article, but also on hollows of the fiber itself composedthe shaped article. Porosity of the fiber depends upon the proportionsof two or more high molecular weight materials in the initial fiber tobe used in making the shaped article. This will be illustrated by thefollowing example.

Chips prepared by blending a 6-nylon and a polystyrene at various mixratio are extruded through a nozzle having 100 holes each of 0.2 mm.diameter to form fibers having different mix ratios, which are stretched300% at 175 C. and then 50% at 200 C. (the total stretch ratio of 500%).The stretched fibers are extracted with benzene at 65 C. to removetherefrom polystyrene. The properties of the porous fibers are asfollows:

And, by buffing the back surface of the obtained synthetic leather thefiber is fibrilized at the buffed part to a very fine denier, and thisimparts to the synthetic leather an excellent leather-like texture.

The method of preparing synthetic leathers according to the inventionwill be further illustrated by the following example which isillustrative rather than limitative of the invention.

A chip consisting of a blend of 40 parts of a 6-nylon and 60 parts of apolystyrene is extruded by means of a screw-type cxtruder through aspinneret with 300 holes each of 0.2 mm. in diameter at spinningtemperature of 300 C. into a draughting zone cooled to a temperature of120 C. by air blast and is Wound up at a rate of 600 m./min. The mixedfiber thus spun is formed crimps of 24/in. and out to a length of 3 cm.and then formed into a three-dimensionalized web of 330 g./m. by meansof a random webber and a needle puncher. The web is lightly compressedby means of hot rollers at 100 C. The so pressed web is immersed in a13% solution in dimethylformamide of a polyurethane type elastic highmolecular weight material obtained by reaction of polyester of adipicacid and ethylene glycol and diphenylmethane diisocyanate and glycol andcoagulated in Water and then dried, and treated with toluene to extractthe remaining solvent and polystyrene in the fiber. The web thus treatedis improved remarkably in pliability and texture as compared with theweb prior to the extraction and has fundamental characteristics asleathers, such as air-retaining property, air-permeability,moisture-permeability and others. As causes for these results may bestated are: that the fiber itself is made more pliant by includingcontinuous and random micro-pores therein as a result of extraction ofthe polystyrene, that in the surface of the fiber the part removedpolystyrene is indented and space is formed between the impregnated highmolecular weight material and the fiber to become movable readily eachother, and that air-permeability, moisture-permeability and air-re-Mixture ratio of polystyrene (percent) 5 1O 20 30 5O 60 80 Fineness 01.)3.0 3.0 a. o a. o a. 1 a. 0 a. 0 e; Before extraction of polystyreneStrength (g./d.)... 7.8 7.6 7.2 6.5 6.0 5.8 5.2

Elongation (percent 21 23 19 23 24 23 22 :13 Fineness (d.). 2.9 2.9 2.92.4 1.9 1.5 1.2 5g After extraction of poly-styrene Strength (g.ld.) 7.27. 5 7. 0 6. 7 6.8 6. 5 6.9 5 m Elongation (percent)- 23 24 25 21 23 2521 g m u Porosity (percent) a 4 6 20 as 49 e0 3 z: 2 2t? 3.0 cu A/B 1.010. 99 1. 00 0.98 0.99 0. 97 0, 98 Z No'rn.-A:Cross-sectional area of thefiber after extraction of polystyrene; BzCross-sectional area of thefiber before extraction of polystyrene.

(in the above table, the porosity indicates value obtained by dividingthe deniers of the fiber after extraction of polystyrene by the deniersof the fiber composed of insoluble components only having the samesectional area as that of the former.)

As evident from the above table, the fiber, which constitutes the shapedproduct of the present invention, has a porosity of up to about 70%.

Furthermore, the remarkable pliability is the charac teristic of thesynthetic leather of the invention.

Generally speaking, in order to form a pliable mat it is desirable touse a fiber having a fine denier because a mat which has been formed ofa fiber having a large fineness results in a rigid synthetic leather.The fine fiber, however, has a defect of having a poor spinnability. Onthe other hand, in the invention there may be used fiber having arelatively large fineness with a good spinnability in the step offorming the mat and there may be obtained by using such a fiber asynthetic leather having the same pliability as that of one obtained byusing a fiber having a small fineness, because of depression in Youngsmodulus caused by extraction and removal of at least one high molecularweight material which constitutes the fiber.

taining property are remarkably enhanced by the presence of thecontinuous hollow. The synthetic leather of the invention thus obtainedhas such external appearance, texture and other properties similar tothose of the natural leather. To say, the synthetic leather of theinvention is composed of a layer of fibers which retains completely thesame fibrous structure as that of the natural leather.

A grain surface, which is a characteristic of the natural leather, maybe formed on a surface of the synthetic leather by applying thereto afilm or the like, and in the invention this may also be performed by thefollowing procedure. To say, a suitable amount of a solution of a highmolecular weight material is applied to a surface of the syntheticleather prepared in the manner as mentioned hereinbefore and iscoagulated in a -wet or dry process. The coagulation preferably isconducted in a wet process, or jointly in a dry process partly and in aWet process mainly.

The high molecular weight material suitably used as coating materialincludes: (1) one or more high molecular weight materials having rubberyelasticity, and (2) mixtures of one or more high molecular weightmaterials having rubbery elasticity and one or more high molecularweight materials having no rubbery elasticity. The term high molecularweight material having rubbery elasticity and high molecular weightmaterial having no rubbery elasticity have the same meanings asmentioned hereinbefore and, as also mentioned above, the solution ofhigh molecular weight material means not only true solution but alsoemulsion.

To the solution there may be added salts, dyes, pigments, fillers,various surface active agents and other additives.

For spontaneous removal and extraction of portion of the high molecularweight material in the impregnating material and of portion of the highmolecular weight material in the grain surface with removal of at leastone high molecular Weight material in the fiber, it is preferalble thatthese three high molecular weight materials are of the same. This,however, is not of necessity.

The removal of portion of the high molecular weight material in theimpregnating material and of portion of the high molecular Weightmaterial coated as grain surface accompanying to the removal of a highmolecular weight material in the fiber imparts to the resultingsynthetic leather more improved characteristics, such as satisfactorypliability and airand moisture-permeabilities. To provide a grainsurface, another preferred embodiment of the invention is as follows. Aproper amount of a high molecular weight material is applied to thesurface of the web or the sheet material in any stage of preparation ofthe synthetic leather and is thereafter coagulated in a dry or wetprocess; specified examples of the modified processes are as follows:

(1) A web of mix-spun fiber is impregnated with a solution of highmolecular weight material and the impregnating material is partly orentirely, coagulated in dry and/ or wet processes, thereafter a solutionof high molecular weight material is applied thereto by coating orspraying to form a grain surface and is then coagulated in dry and/orwet processes. Then the web is soaked in a solvent for at least one highmolecular weight material in the mix-spun fiber to extract therefrom thesaid high molecular weight material, and washed and dried.

(2) A web of mix-spun fiber is impregnated with a solution of highmolecular weight material and, thereafter, a solution of high molecularweight material is applied thereto by coating or spraying to form agrain surface. Then the both high molecular weight materials arecoagulated in dry and/or wet processes. At least one high molecularweight material in the mix-spun fiber is extracted therefrom and the sotreated web is washed and dried.

(3) A web of mix-spun fiber is impregnated with a solution of highmolecular weight material and the high molecular weight material iscoagulated in a Wet process. The Web is then washed and dried and,thereafter, a solution 01f high molecular weight material is appliedthereto by coating or spraying to form a grain surface.

Then at least one high molecular weight material in the mix-spun fiberis extracted therefrom and the so treated web is washed and dried.

Even if a solution of high molecular weight material is appliedrelatively thick on formation of the grain surface by coating orspraying of the high molecular weight material, the resulting syntheticleather has satisfactory airand moisture-permeabilities, such propertiesbeing important characteristics of leathers, because portion of theapplied high molecular weight material is removed by extraction in asubsequent step of the process, and the removal of portion of the highmolecular weight material results in formation of a moderate indentionwhich makes the resulting synthetic leather very similar in externalappearance to the natural leather.

The grain surface may also be obtained by forming a Web with a mix-spunfiber made from a blend of high molecular weight material having rubberyelasticity and a high molecular weight material having no rubberyelasticity, laminating the said Web on a synthetic leather of theinvention as already mentioned above and, thereafter, completely oralmost completely dissolving said high molecular weight materials insaid Web and, thereby, bonding said web to said synthetic leather.

In the manufacture of the synthetic leather of the invention, there maybe added, if desired, a step of partially dissolving the unextractablehigh molecular weight materials in the mix-spun fiber to adhere thefibers to other fibers.

Furthermore, the mix-spun fiber of a raw material for the syntheticleather of the invention may be used in admixture with a proportion ofvarious fibers comprising monopolymer or natural fibers. In themanufacture of the synthetic leather or like shaped articles of theinvention, a woven fabric composed of a synthetic fiber consisting ofmonopolymer, or natural fiber may be used as a core layer or substratum.

According to the invention, the two steps of coagulation and ofextraction may be conducted simultaneously.

The present invention will be illustrated by the following exampleswhich are by no means limitative.

EXAMPLE 1 A stretched and crimped nylon-polystyrene 40:60 mixspunfilament of 2 denier was cut into a staple fiber of 5.0 cm. length andthe staple fiber was formed by random webbing and subsequent needlepunching into a nonwoven mat of a weight of 220 g./m. The non-woven matthus formed was immersed in an impregnating solution prepared by adding0.4% of cellulose octadecylurethane as softener to a 8% solution indimethylformamide of a polyurethane elastomer obtained by reaction of apolyethylene propylene adipate of a molecular weight of 1,500 (moleratio of ethylene glycol units to propylene glycol units of 07:03),p,p-diphenylmethane diisocyamate and ethylene glycol in the mole ratioof 1:2.5:1.5, and then squeezed by means of doctor blades at each sideof the mat to adjust the amount of the solution taken up by the mat toabout eight times the weight of the mat. A 10% solution of saidpolyurethane in dimethylformamide, in the amount of four times theweight of the fibrous mat, was coated to surface of the so impregnatedmat. The mat was then immersed in a 30% aqueous solution ofdimethylformamide at 30 C. for a period of 15 minutes and squeezed whilecoagulating the impregnating and coated materials, and then Washed withwater for a short period of time, after which was passed through hotpress rollers and then extracted and removed at least of polystyrene inthe nylon-polystyrene mix-spun fiber by toluene at 70 C.

The sheet material thus obtained was extremely pliant due to pooradhesion between nylon fibers and poly urethane elastomer and presenceof random micro-pores which had been formed in the nylon fibers as aresult of extraction of polystyrene, and possessed a smooth texture. Thegrain surface of the sheet material was extremely tough due to presenceof fibers and was fine-grained and pliant, and possessed a texturesimilar to that of natural leather, especially those for wear uses. Theproperties of the sheet material were similar to those of sheep skin asshown in the following table.

Synthetic Sheep leather of (Suede) Sheep the invention Weight (g./m. 213269 218 Thickness (mm) 0.68 0.53 0. 64 Apparent specific grav y (g./em.0. 45 0. 51 0. 34 Tensile strength (kg/3 cm.) 22. 4 21. 4 5.8 Tensilestrength (kg/mm?) 1 1. 1OX1. 09 1. 35 0.30 Elongation (percent) 75. 039. 5 44.9 Tear strength (kg.) 3.0 1. 4 2. 0 Surface wear property (t e)12 219 Rub resistance (time) 1, 000-2, 000 500-1, 000 1, 000-2, 000Rigidity (mm) 45 52 27 Water content (percent) 15 14 14 Degree of waterproof (cm) 143 225 Air-permeability (see) 41 19 48 Moisture-permeability(glmfi/day) 8, 490 8, 220 7, 310

1 Longitudinalxlateral.

1 1 EXAMPLE 2 A non-woven mat of a weight of 330 g./m. composed of anylon-polystyrene 40:60 mix-spun fiber of 5.0 cm. length and of 3.0denier, was immersed in a impregnating liquid prepared by adding to a13% solution of a polyurethane elastomer as in Example 1 indimethylformamide 2.5% of sorbitan monostearate and 3% of each carbonblack and titanium dioxide, and squeezed at both sides by means ofdoctor blades to adjust the amount of the liquid impregnated to from tento eleven times the weight of the fibrous mat. A 20% solution of apolyurethane elastomer in dimethylformamide, in the amount 2.5 times theweight of the fibrous mat, was coated to the surface of the soimpregnated mat. The mat was then immersed in a 30% aqueous solution ofdimethylformamide for 20 minutes to coagulate and, thereafter, extractedpolystyrene in the fiber by toluene at 6570 C. The sheet material thusobtained was of an apparent specific gravity of 0.5-0.6 and possessed acompact texture. In addition, the sheet material possessed a moderatepliability due to poor adhesion between resin and fibers and presence infibers of random micro-pores resulting from the extraction, andexhibited a texture similar to that of the natural leather for shoeupper use. The properties of the sheet material were as shown in thefollowing table.

12 EXAMPLE 5 A blend of 50 parts of polyethylene terephthalate and 50parts of polystyrene was melt spun by means of an extruder intofilaments, and hot drawn by 5 times to obtain a 2 denier filament. Thefilament was formed into a web with a three-dimensional networkstructure by the same manner as in Example 3. The web was impregnatedwith a 6% solution obtained by dissolving a mixture of 60 parts of apolyurethane-type high molecular weight material as in Example 1 and 40parts of a polystyrene in dimethylformamide and, thereafter, a 5%solution obtained by dissolving a mixture of 40 parts of a polyurethanetype high molecular weight material, parts of a polyvinyl chloride and30 parts of polystyrene in dimethylformamide was again sprayed to grainsurface of the impregnated web. The web was then coagulated by water andtreated in toluene at 80 C. to completely extract polystyrene in theresulting shaped article which was then washed with methanol and dried.

EXAMPLE 6 This Cowhide Cowhide invention (Chrome (lacquer Shoe upper)finishing) Weight (g./m. 880 553 1, 160 Thickness (mm.) 1. 43 0. 96 1.80 Specific gravity (g./cm. 0.61 0. 58 0. 64 Tensile strength (kg/3 cm.)55 57 88 Tensile strength (kg./mm. 1 1. 28X1.2 1.97 1. 63 El ongation(percent) 58x57 57 74 Remaining strain (1 time) percent 1. 2 1. 8 2. 5Remaining strain (10 times) percent. 2.0 2. 4 3.8 Tear strength (kg.) 3.3 3.2 5. 3 Rule resistance (time) Air p enneability (min) 30 3 Moisturepermeability (g./m. /24 hours) 1, 280 2, 580 530 1 LongitudinalXlateral.

B More than 10,000. a 3 More than 2 hours. 1

The sheet materials as shown in the above examples may be dyed, orapplied a smooth surface by known method such as dyeing, spraying,coating or laminating a solution or emulsion of a high molecular we htmaterial or embossing or otherwise finishing.

EXAMPLE 3 A blend of 50 parts of a 6-nylon and 50 parts of a polystyrenewas melt spun by means of extruder into filaments and stretched by 6times to obtain a mix-spun fiber of 1.5 denier, which was wound andcrimped to 18/in., cut into 50 mm. length and, thereafter, passedthrough a random webber and a needle loom to form a web with athree-dimensional network structure. The web was impregnated with a 6%solution in tetrahydrofuran of a polyurethane prepared by reacting apolyester derived from adipic acid and ethylene glycol withdiphenylmethane dissocyanate to form a prepolymer and subsequentlyreacting the prepolymer with a diol, and was then immersed in water tocoagulate the polyurethane. After dried, the shaped article thus formedwas immersed in toluene at 90 C. for one hour to extract polystyrene,then washed with methanol and dried. The finished shaped article of theinvention was a pliable leather-like product with a high elasticity.

EXAMPLE 4 Single surface of the pliable shaped article, as obtained inExample 3, was burned and the shaped article was then hot pressed. Thena 7% solution of a polyurethane type high molecular weight material asused in Example 1 in dimethylformamide was applied by spraying to theburnt surface of the shaped article to form a very thin coating film.Thus, there was obtained a synthetic leather just like natural leather.

g./m. was obtained by means of a random webber and a needle puncher. Theweb was, after hot pressed by means of hot rollers, impregnated with a6% solution of a polymethylacrylate in toluene and squeezed by means ofru ber rollers to adjust the amount of the solution taken up by the webto 600% by weight of the web. The solution was, thereafter, sprayedagain to the surface and the web was coagulated, while squeezing, inwater at C. and then extracted polyvinyl alcohol by standing the web inwater at 90 C. and, subsequently washed sufiiciently with water andmethanol. The synthetic leather of the invention thus obtained wassimilar in external appearance, texture and other properties to those ofnatural leather.

EXAMPLE 7 A mix-spun filament (1.5 denier) formed of a blend of parts ofa polystyrene and 50 parts of a polyethylene terephthalate was formedcrimps of 20/in. and cut into 3 cm. length. The staple fiber thusobtained was formed, in the same manner as in Example 6, into athree-dimensionalized random web with a weight of 250 g./m. The web wasimpregnated with a 6% solution in dimethylformamide-acetone (121) of apolyurethane type high molecular weight material prepared by reacting apolyethylene adipate with diphenylmethane diisocyanate to form aprepolymer and reacting the prepolymer with a diol and, thereafter, theweb was squeezed by means of rubber rollers so as to adjust the amountof the solution taken up by the web to 600% by weight of the web. Thesolution was then applied again to the surface of the web and the webwas, after stood still for a short period of time, coagulated by 30%aqueous dimethylformamide solution, while squeezing. The shaped articlethus formed was immersed in toluene at 80 C. for minutes to effectcomplete extraction of polystyrene in the mix-spun 13 fiber, and thenwashed and dried. The artificial leather thus obtained possessed thesame external appearance, texture and other properties as that ofnatural leathers.

EXAMPLE 8 A mix-spun filament composed of a blend of 40 parts of a6-nylon and 60 parts of a polyvinyl alcohol was stretched by 6 times at200 C. to obtain a fiber of 1.5 denier. The filament was formed crimpsof 18/in. and cut into 50 mm. length and, thereafter, passed through arandom webber and a needle loom to form a web with a three-dimensionalnet-work structure. The web was impregnated with a 6% solution indirnethylformarnide of a polyurethane prepared by reacting polyesterobtained from ethylene glycol and adipic acid with a diphenylmethanediisocyanate and a diol and then immersed in water so as to elfectcoagulation of polyurethane and at the same time extraction of polyvinylalcohol contained in the mix-spun fiber and was, thereafter, washedagain with water and dried. The shaped article of the invention thusobtained was an extremely pliant leather-like product with a highelasticity.

EXAMPLE 9 A mix-spun filament of 2 denier obtained by melt spinning ablend of 45 parts of a polyester derived from terephthalic acid andethylene glycol and 55 parts of a polystyrene by an extruder and hotdrawing by 5 times.

The fiber was formed into a web with a three-dimensional networkstructure in a manner as in Example 8 and the web was impregnated with a6% solution of a blend of 60 parts of a polyurethane type high molecularweight material as in Example 1 and 40 parts of a polystyrene indimethylformamide. Then a 5% solution of a blend of 40 parts of apolyurethane type high molecular weight material, 30 parts of apolyvinyl chloride and 30 parts of polystyrene in dimethylformamide wassprayed to the grain surface and, thereafter, the web was treated incyclohexane at 50 C. to remove completely polystyrene and coagulatepolyurethane in the shaped article and then was washed with methanol anddried.

What we claim is:

1. A method for the manufacture of pliant, supple, airandmoisture-permeable sheet material, comprising:

(a) impregnating a fibrous substrate with a solution of high molecularweight material selected from the group consisting of:

(i) at least one polymeric substance having rubber-like elasticity, and(ii) a mixture of at least one polymeric substance having rubber-likeelasticity with at least one polymeric substance not having rubber-likeelasticity, said fibrous substrate being comprised of mix-spun fibersshaped from polymers comprising at least two high molecular weightmaterials'selected from the group consisting of polyamide, linearcondensation polyester, polymethacrylate, polyvinyl ester, polyvinylalcohol, derivatives of polyvinyl alcohol, polyolefin, atactic andisotactic polystyrene, alkyl-substituted polystyrene,halogen-substituted polystyrene, polvinyl halide, polyacrylonitrile, andpolyvinylidene halide;

(b) coagulating the impregnant; I

(c) thence extracting at least one of the polymers comprising themixspun fibers by means of a solvent therefor which is a non-solvent forat least one other polymer in the said mix-spun fibers; and

(d) there being initially present in the said mix-spun fibers from about10 percent to about 60 percent by weight of the polymeric materialextracted according to step (c).

2. The method as defined by claim 1, wherein the high molecular weightmaterial (i) is at least one member selected from the group consistingof elastomeric segmented polyurethane, polyacrylate, synthetic rubber,chlorinated polyolefin and chlorinated polyethylene, and further whereinthe high molecular weight material (ii) is a mixture of the above highmolecular weight material (i) with at least one member selected from thegroup consisting of polyvinyl chloride, polyacrylonitrile, polystyrene,polyvinyl alcohol, acetalized polyvinyl alcohol, polyvinyl acetate,polyamide, polypropylene, polyethylene, nonelastomeric polyurethane,polyurea, linear condensation polyester and polycarbonate.

3. The method as defined by claim 2, further comprising providing agrain surface characteristic of leather on the sheet material byapplying thereto a coating of a high molecular weight material selectedfrom the group consisting of:

(i) at least one polymeric substance having rubberlike elasticity, and

(ii) a mixture of at least one polymeric substance having rubber-likeelasticity with at least one polymeric substance not having rubber-likeelasticity.

4. The method as defined by claim 2, wherein the mixspun fibers areIbi-component.

5. The method as defined by claim 2, wherein the coagulation andextraction are effected simultaneously.

6. The method as defined by claim 2, wherein the impregnant is itselfextracted to some extent by the solvent employed in step (c).

7. The method as defined by claim 2, wherein the solvent of step (c) isselected from the group consisting of: water, an aromatic hydrocarbon, acyclic ether, an aliphatic hydrocarbon, an aliphatic ketone, a cyclicketone, and a methanol solution of calcium chloride, titaniumtetrachloride and lithium chloride, and mixtures thereof.

8. The method as defined by claim 2, wherein the solution of step;(a) isa true solution.

9. The method as defined by claim 2, wherein the solution of step (a) isan emulsion.

10. The method as defined by claim 2, wherein the fibrous substrate is anon-woven batt.

11. The method as defined by claim 2, wherein the fibrous substrate hasbeen mechanically compressed.

12. The method as defined by claim 2, wherein the mixspun fibers of thefibrous substrate have been shrunk.

13. The method as defined by claim 2, wherein the fibrous substrate isformed from mix-spun fibers obtained by mixed spinning of at least twopolymers.

14. The method as defined by claim 2, wherein the impregnated sheetmaterial is pressed prior to coagulation.

15. The method as defined by claim 2, wherein the impregnated sheetmaterial is pressed during coagulation.

16. The method as defined by claim 2, wherein the impregnated sheetmaterial is pressed subsequent to coagulation.

17. The method as defined by claim 3, wherein the high molecular weightmaterial (i) is at least one member selected froh'i the group consistingof elastomeric segmented polyurethane, polyacrylate, synthetic rubber,chlorinated polyolefin and chlorinated polyethylene, and further whereinthe high molecular weight material (ii) is a mixture of the above highmolecular weight material (i) with at least one member selected from thegroup consisting of polyvinyl chloride, polyacrylonitrile, polystyrene,polyvinyl alcohol, acetalized polyvinyl alcohol, polyvinyl acetate,polyamide, polypropylene, polyethylene, nonelastomeric polyurethane,polyurea, linear condensation polyester and polycarbonate.

18. The method as defined by claim 3, wherein the high molecular weightmaterial used for the coating is of the same type used as theimpregnant.

19. The method as defined by claim 3, wherein the impregnant and thesurface coating are themselves extracted to some extent by the solventemployed in step (c).

20. The method as defined by claim 4, wherein the mixspun fibers arecomposed of poly-(e-caprolactam) and polystyrene.

21. The method as defined by claim 4 wherein the denier of the mix-spunfibers ranges from between about 1.5 and 3.0, and further wherein suchfibers are composed of poly (e-caprolactam) and polystyrene.

22. The method as defined by claim 11, wherein the fibrous substrate hasbeen heated during compression.

23, The method as defined by claim 17, wherein the grain surface isprovided by applying to a surface of the sheet material, subsequent tothe extraction step (c), a solution of the high molecular weightmaterial and thence coagulating such coating.

24. The method as defined by claim 17, wherein the grain surface isprovided by applying to a surface of the sheet material, prior to theextraction step (c), a solution of the high molecular weight materialand thence coagulating such coating.

25. The method as defined by claim 17, wherein the grain surface isprovided by applying to a surface of the sheet material, prior tocoagulation step (b), a solution of the high molecular weight materialand thence simultaneously coagulating such coating and the impregnant.

26. The method as defined by claim 19, wherein the three high molecularweight materials are the same.

27. The method as defined by claim 21, wherein the impregnation of step(a) is with a solution of an elastomeric segmented polyurethane indimethylformamide.

28. The method as defined by claim 27, wherein the polystyrene isextracted according to step (c) with toluene.

References Cited UNITED STATES PATENTS 2,773,286 12/1956 Piccard et al.

3,310,505 3/1967 Parker 260--2.5

WILLIAM D. MARTIN, Primary Examiner.

THEODORE G. DAVIS, Assistant Examiner.

US. Cl. X.R.

